Iontophoresis is a method for delivering a drug across a biological membrane, such as the skin or, in the case of certain ear surgery procedures, the tympanic membrane (TM). By applying low-level electrical current to a similarly charged drug solution, iontophoresis repels ions of the drug, thus transporting them across the skin or other membrane. In ear procedures, attempts have been made in the past to use iontophoresis to anesthetize (or “numb”) a TM before placing an ear tube across it to treat chronic ear infections. For TM iontophoresis, a drug solution is placed in an ear canal and current is applied to the solution, thus transporting the anesthetizing drug across the TM.
In theory, iontophoresis should be ideal for numbing a TM, because it would allow drug to be transported across the full thickness of the TM, would focus the drug delivery on the TM and the surrounding ear canal, and would not require a painful injection with a needle. Iontophoretic drug delivery to the TM has proven challenging, however. Companies such as Xomed, Inc. (Medtronic Xomed, Inc.) and Otomed, Inc. (Lake Havasu City, Ariz.) have previously provided iontophoresis systems for anesthetizing TMs, but these systems and their associated methods have had a number of significant drawbacks. Most significantly, it has been very challenging, using previous iontophoresis systems, to provide adequate anesthesia to the TM without causing significant pain and discomfort to the patient in the process. Although the pain and discomfort caused by applying current to an iontophoretic solution in the ear canal may range from mild to severe, even mild pain or discomfort may make an ear tube placement procedure intolerable for pediatric patients and even some adult patients.
To drive a drug solution across a TM via iontophoresis, the solution must have certain characteristics to allow it to be transported, and current must be applied in such a way to cause the transport. Previously used iontophoresis solutions for TM anesthesia were generally mixtures of lidocaine and epinephrine, often having a pH range of about 5.2-5.9, and this pH range was thought to be optimal for iontophoretic drug delivery. Once the solution is in place in the ear canal, a sufficient amount of current must be applied for a sufficient amount of time to transport the anesthetizing drug across the TM. Unfortunately, with previously available systems, the combinations of drug solution and current application were typically at least uncomfortable and often quite painful. Attempts to decrease the pain caused by iontophoresis generally resulted in unsatisfactory drug delivery.
Placement of ear tubes through the TMs for treating chronic ear infections is one of the most common ear, nose and throat (“ENT” or “otolaryngology”) surgical procedures requiring general anesthesia in children. Although tube placement is a relatively routine procedure, it almost always requires general anesthesia when performed on children, since they are usually unable to tolerate the pain and discomfort associated with numbing the tympanic membranes for the procedure. Unfortunately, general anesthesia carries a number of risks, some of which are still unknown and being researched. Adult patients sometimes undergo ear tube placement with topical applications of local anesthesia (such as phenol), thus avoiding general anesthesia, but oftentimes such a procedure is quite painful or at least very uncomfortable, due to unsatisfactory methods of numbing the TMs. Therefore, it would be highly advantageous to provide a method for anesthetizing TMs and surrounding ear tissue that would eliminate the need for general anesthesia and that would be palatable to patients.
Therefore, a need exists for improved iontophoretic methods and systems. Ideally, such methods and systems would facilitate iontophoretic drug delivery across a tympanic membrane for ear tube placement or other surgical procedures in the ear. Also ideally, such methods and systems would minimize or eliminate any pain caused by the iontophoresis process. At least some of these objectives will be met by the various embodiments of the present invention.